Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

825
FXUS63 KLOT 041155
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
655 AM CDT Sat Jul 4 2026

.KEY MESSAGES...

- Periods of showers and thunderstorms will continue through
  Sunday. A few storms could be strong to severe with a threat
  for damaging winds especially today near and south of I-80.

- Locally heavy rainfall will also accompany any thunderstorms
  and may result in flash flooding especially if storms develop
  over areas that received heavy rain the past couple days.

- Drier and more seasonable conditions expected to start the
  week before stormier weather returns late week.

&&

.DISCUSSION...
Issued at 312 AM CDT Sat Jul 4 2026

A decaying line of showers and thunderstorms continues to drift
across north-central IL and northwest IN early this morning.
These showers/storms are expected to continue to wane from north
to south by daybreak leaving the area with dry conditions to
start the day. However, there is a cluster of thunderstorms in
central IA that, if it holds together, would move into the
western portions of the forecast area by mid-morning. While
latest forecast guidance continue to show this cluster
weakening and dissipating prior to arriving, the decent
organization noted on radar and the fact that instability should
be increasing as this cluster moves east supports the idea that
the storms may survive into portions of northern IL. Despite
the lower confidence on the storm`s evolution, have opted to
introduce some 20-40% POPs for areas near and north of I-80
through the morning to tease the potential for this cluster to
make it into the area. If the storms do survive the main threat
with them will be lightning strikes and locally heavy downpours,
but some locally gusty winds cannot be ruled out either.

Regardless of how the morning storms pan out, the shortwave
trough in NE and its associated cluster of storms is expected to
move into northern IL and eventually northwest IN this
afternoon and linger through the early evening hours. Given the
much better environment forecast for this afternoon this second
cluster will have no problems making it into the area. The only
question with it is how could the morning storms alter the
environment in our northern CWA to perhaps make storm coverage
or intensity slightly lower there. At this time the thinking is
that a line of scattered thunderstorms will move across the
entire area between the hours of 1-8 PM (plus or minus an hour)
and last about 2-3 hours at any one location. While wind shear
today is not as good as yesterday (only around 20- 25 kts) the
decent instability and forcing from the shortwave may support a
few strong to severe storms capable of producing damaging winds
especially near and south of I-80 where SPC has their level 1 of
5 severe risk. In addition to the gusty wind threat, these
storms will be capable of heavy downpours that may result in
more flash flood, particularly in areas that have seen heavy
rain over the past couple of days.

Once the line of storms moves through this evening there is a
decent signal for a period of tranquil weather for the later
portion of the evening. Should this hold true it looks as if we
may get a break just in time for July 4th fireworks. With the
shortwave still expected to be pivoting overhead some isolated
to widely scattered showers/storms cannot be ruled out at times
overnight, but most areas should be dry. However, the
combination of light winds and ample low-level moisture does
look to support a period of patchy fog tonight into Sunday
morning. Since confidence on fog coverage and location is rather
low and will be dependent on storm trends this afternoon (where
the best moisture resides from the rain) and inland progress
from Lake Michigan, have opted to forego a formal fog mention
in the forecast for now.

Heading into Sunday, another shortwave trough is progged to dig
out of the northern Plains and phase with the aforementioned
shortwave that is expected to still be lingering over the Great
Lakes. The phasing of these troughs should allow upper-level
heights to deepen and give way to more scattered showers and
thunderstorms Sunday afternoon. Recent CAM guidance trends have
started to indicate that the deepening trough overhead should
allow a weak surface low to develop in central IL and traverse
towards central IN Sunday afternoon. If this does occur then it
seems that the better instability should stay more into the
southern portions of our area (if not fully south of us) and
therefore limit shower/storm coverage with northward extent.
Though, if the low develops further north then more of the area
could see showers and storms once again. For now have opted to
keep some 30-50% POPs areawide (highest values south of I-80)
for this potential but suspect these will be able to get refined
in future forecasts. Outside of the rain chances, temperatures
on Sunday will be a tad cooler (highs in the lower to mid-80s)
due to east-northeast winds. In fact highs near the lake on
Sunday may struggle to get out of the 70s.

By Monday the upper trough will be ejecting eastward and taking
with it the chances for showers and thunderstorms as a surface
high settles into the western Great Lakes. It should be noted
that our official forecast does have some 20-30% POPs in our far
southern CWA Monday afternoon where some slower guidance has a
stray shower/storms trying to develop, but the overall
environment locally should support dry conditions areawide so
suspect these POPs will get removed in future updates.
Nevertheless, temperatures on Monday will be on the seasonable
side with highs once again in the lower to mid-80s inland with
70s expected near the lake due to onshore winds. Tuesday will
feature similarly dry conditions, but with slightly warmer
conditions (highs in the mid to upper 80s) as winds turn back
southerly.

Unfortunately the tranquil weather is not forecast to last long
as guidance continues to show the return of west-southwest flow
aloft for the middle and latter half of next week. While
temperatures look to remain seasonable, humidity will be on the
increase which will also bring the return of shower and
thunderstorm chances.

Yack

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 655 AM CDT Sat Jul 4 2026

Key aviation forecast messages:

- First round of storms to move through this morning.

- Greater coverage of storms favored this afternoon into early
  evening, some potentially strong.

- Low confidence in wind direction trends today, eventually
  turning NE behind a lake breeze in the afternoon.

- Potential for fog/low stratus off the lake late tonight into
  early Sunday AM.

The thunderstorm complex over central Iowa, while weakening, has
managed to hold together into northwest Illinois. Have
accordingly introduced TEMPO groups for TSRA into the Chicago
area terminals for mid to late morning period (14-16Z at
ORD/MDW), though some slowing can`t be ruled out which may
require shifting that later by an hour.

Given the initial round of storms is not handled well in model
guidance, how things evolve into this afternoon remains lower
confidence overall. An MCV feature over south central Iowa may
serve as the focus for additional thunderstorm development this
afternoon. Given its slower movement have shifted the TEMPOs for
TSRA back an hour at most sites to when greater coverage of
showers and storms is favored (19-23Z). Diminishing coverage is
then expected heading into the mid to late evening hours. Have
maintained dry TAFs through the remainder of the TAF period
though a stray shower or storm can`t be ruled out.

Wind directions are expected to remain highly variable through
midday before a lake breeze moves inland in the afternoon
turning winds more solidly northeast, though this could end up
being delayed by any convection that occurs this afternoon.

Lastly there is a signal for fog (potentially dense) and/or low
stratus (IFR/LIFR) over Lake Michigan that may try to ooze
inland late this evening through early Sunday morning.
Confidence remains too low to include with this update but will
be monitored closely given it may also have some dependence on
how convective trends also evolve later today.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago